Background and objective: Living in a farm environment has been reported to be associated with lower prevalence of asthma, based on the results of cross-sectional studies. The objective of this longitudinal study was to determine whether living in a farm environment is associated with lower incidence of asthma among children.
Methods: A total of 13 524 asthma-free children aged 0–11 years were drawn from the Cycle 1 (1994/1995) of the Canadian National Longitudinal Survey of Children and Youth (NLSCY). Subjects were categorized as dwelling in rural farming, rural non-farming and non-rural environments. Incidence of physician-diagnosed asthma was determined at Cycle 2 (1996/1997). Bootstrap logistic regression method was used to adjust for design effect in the NLSCY.
Results: The 2-year cumulative incidence of asthma was 2.3%, 5.3% and 5.7% among children living in farming, rural non-farming and non-rural environments, respectively. From the multivariate analysis with adjustment for important confounders, children from a farming environment had a reduced risk of asthma compared with children from rural non-farming environment with odds ratios (OR) of 0.22 (95% CI: 0.07–0.74) and 0.39 (95% CI: 0.24–0.65) for children with and without parental history of asthma, respectively. Children living in a non-rural environment with parental history of asthma had an increased risk of asthma incidence when compared with children living in rural non-farming environment (OR = 2.51, 95% CI: 1.56–4.05).
Conclusion: This longitudinal study expands on observational study results which suggest a reduced risk of developing asthma associated with living in a farming environment.